This invention relates in general to techniques and apparatus improving combustion and heat extraction in units using solid type fuel, such as stoves, furnaces and combustion chambers.
Heretobefore, solid type fuel burning units have used a natural flow of primary air upward through a fire bed to support the combustion process. In order to develop and continue combustion in prior-art units using a natural draft system, high temperature exhaust gases are required to move from the combustion process into and up a vertical chimney to develop a partial vacuum in the combustion chamber to draw in air to sustain combustion. This natural draft system results in a continuous waste of high cost heat energy which cannot be used for useful heating purposes.
Also, these prior-art units use a primary source of air which flows up through the fire bed from below, allowing burnt and unburnt gases to escape without complete combustion. In addition to limiting the burning efficiency of the unit, these partially burnt exhaust gases can cause chimney problems by cooling and forming `creosote` deposits on the walls of the chimney. This can result in a fire and safety hazard if not periodically removed.
In the prior-art, numerous attempts have been made to increase the burning efficiency of heating units. Down-drafting has been attempted wherein a secondary flow of air is introduced above the fire bed, forcing combustion gases back toward the fire bed. Because of the upward flow of primary air, these combustion gases usually exit at the top or sides of the fire bed. While this method has resulted in some increase in burning efficiency, it still does not take full advantage of the genuine down-draft developed by Benjamin Franklin, the principal of which uses the primary source of air entering above the fire bed and exiting below the grate, and then flowing downward and through the fire bed for optimum heat release of solid fuel and volatile energies. These prior-art units still require a vertical chimney for draft development.
Any annual heating bill includes numerous hidden costs, such as for the purchase and maintenance of the heating unit and required accessories plus the uncertain heat return per fuel cost dollar. As an example, a conventional heating device demands a vertical chimney as a necessary component of the burning progression; and this component is costly to construct, maintain and repair. These hidden investments must be added to the annual fuel bill. In addition, these costs are substantially increased by the fact that a conventional wood burning stove is acknowledged to be only about 50% or less fuel return efficient, partly because heat is continually wasted to generate an elevated temperature of about 204.degree. Celsius to create a natural chimney draft, and a goodly portion of unburnt volatile energy goes up the chimney without contributing to useful heating.